The present invention generally relates to a semiconductor device in which a metal wiring is formed so as to be electrically connected to an electrode of a semiconductor element and a part of the metal wiring is used as an external electrode, and a manufacturing method of the same. More particularly, the present invention relates to a semiconductor device having excellent junction reliability between a metal wiring and a ball electrode mounted to an external electrode portion of the metal wiring, and a manufacturing method of the same.
With recent reduction in size and improvement in functions of electronic equipments, an increasing number of input/output (I/O) pins is formed in a semiconductor element, and therefore the pitch of electrodes is reduced.
Especially in a CSP (Chip Size Package) type semiconductor device, electrodes of a semiconductor element are formed by a dry etching method in a diffusion process, whereas wiring electrodes of a substrate on which the semiconductor element is mounted are formed by a wet etching method in an assembling process. Accordingly, the pitch of the wiring electrodes of the substrate on which the semiconductor element is mounted is necessarily greater than that of the electrodes of the semiconductor element. In view of this, a semiconductor device is increasingly developed which deals with the difference between the electrode pitch of the semiconductor element and the wiring-electrode pitch of the substrate. In such a semiconductor device, metal wirings are formed so as to be electrically connected to the respective electrodes of the semiconductor element and a part of each metal wiring is used as an external electrode in order to increase the distance between the external electrodes.
Hereinafter, a conventional semiconductor device will be described with reference to the figures.
FIG. 15A is a perspective plan view of the conventional semiconductor device. FIG. 15B shows an example of the cross-sectional structure taken along line XV—XV of FIG. 15A. FIG. 15C shows another example of the cross-sectional structure taken along line XV—XV of FIG. 15A.
As shown in FIGS. 15A and 15B, electrodes 2 are formed on the surface of a semiconductor element 1. A passivation film 3 is formed over the surface of the semiconductor element 1. The passivation film 3 is formed from silicon nitride (SiN) or the like, and has an opening on each electrode 2. Metal wirings 4 are formed on the passivation film 3. Each metal wiring 4 is formed from copper (Cu) and electrically connected to a corresponding one of the electrodes 2. A solder resist film 5 is formed on the metal wirings 4 and the passivation film 3. The solder resist film 5 has an opening on a portion of each metal wiring 4 which functions as an external electrode (hereinafter, referred to as “external electrode portion”). In order to electrically connect the electrodes 2 formed on the surface of the semiconductor element 1 to wiring electrodes of a substrate (not shown) on which the semiconductor element 1 is mounted, respectively, a ball electrode 6 formed from solder is connected in a molten state to each opening of the solder resist film 3, that is, to the external electrode portion of each metal wiring 4.
As shown in FIG. 15C, an insulating resin layer 7 may be formed between the semiconductor element 1 having the passivation film 3 thereon and the metal wirings 4.
In each of the forms of the conventional semiconductor device described above, the wiring electrodes of the substrate on which the semiconductor device is mounted are respectively connected to the metal wirings 4 of Cu formed on the surface of the semiconductor element 1 through the ball electrodes 6 formed from solder. In other words, when the metal wirings 4 are formed from Cu (which is a commonly used metal wiring material), metal junction of Cu (the metal wirings 4) and solder (the ball electrodes 6) is formed at the boundary between the metal wiring 4 and the ball electrode 6.
In the above conventional semiconductor device, however, tin (Sn) contained in solder of the ball electrode 6 diffuses into Cu of the metal wiring 4 to form a Sn—Cu alloy layer. As a result, in the portion of the metal wiring 4 on which the ball electrode 6 is mounted (i.e., the external electrode portion) and the portion near the external electrode portion, the Sn—Cu alloy grows in the most part of the metal wiring 4. The Sn—Cu alloy is weak and hard. The semiconductor device 1, the resin film covering the surface of the semiconductor element 1 and the substrate have different thermal expansion coefficients. Accordingly, when the temperature is varied to melt the ball electrodes in the process of mounting the semiconductor device onto the substrate, stresses are generated due to such a difference in thermal expansion coefficient. Accordingly, the Cu—Sn alloy layer formed in the portion of the metal wiring 4 to which the ball electrode 6 is mounted is likely to be broken by the stresses.